1. Field of the Invention
This invention relates to nonionic-hydrophilically modified polyisocyanate compositions containing urethane groups based on 2,4-and/or 2,6-diisocyanatotoluene, to a process for their production, to two-component polyurethane coating compositions containing the polyisocyanate compositions and to their use for the production of coatings on water-resistant substrates.
2. Description of the Prior Art
In surface technology, ecologically safe lacquers and coating compositions are becoming increasingly more important. The important problem in this regard is to reduce the quantities of organic solvents used in lacquers and coating compositions. An important contribution towards solving this problem has been made by the recently developed water-based polymer dispersions and the recently developed water-based two-component polyurethane coating compositions. These latter compositions, in the same way as the corresponding solvent-based, two-component polyurethane coating compositions, enable high-quality lacquer coatings to be produced.
These two-component polyurethane coating compositions are described, for example, in EP-A-0,358,979, EP-A-0,543,228 and EP-A-0,542,105 and in the PCT applications with the publication numbers 9305087 and 9309157. Of particular importance in this regard are the systems according to EP-A-0,358,979 based on selected water-soluble or water-dispersible polyacrylate resins and preferably low molecular weight aliphatic lacquer polyisocyanates. The lacquers according to these prior publications dry relatively slowly so that they are of only limited use for applications where rapid drying is a critical requirement, for example, in wood and furniture coatings.
The same also applies to the two-component systems according to Japanese patent application 58-66736 published under number 191770/1984. According to applicants' own investigations, the coating compositions described in this prior publication show totally inadequate film-forming properties (matt films with serious surface defects are always obtained), in addition to which drying times of 3 days are necessary, even when aromatic polyisocyanates are used, as can be seen from the examples.
Accordingly, an object of the present invention is to provide new water-based two-component polyurethane coating compositions which would have an acceptable pot life, but harden at room temperature just as quickly as known solvent-based, two-component polyurethane coating compositions.
It has now surprisingly been found that this object may be achieved by using the polyisocyanate compositions according to the invention described in detail hereinafter as the polyisocyanate component in water-based two-component polyurethane coating compositions described hereinafter.